King for a day ... Selma’s David Oyelowo is to play the exiled leader of Bechuanaland in a new drama from Belle’s Amma Asante.
Photograph: Richard Shotwell/Invision/AP

He was an Oxford-educated African king, while she was a white Englishwoman working as a clerk at Lloyd’s of London. Now their 1948 marriage, which caused scandal in Apartheid-stricken South Africa and the British protectorate of Bechuanaland (later Botswana), is to be the subject of a new period drama starring Britain’s David Oyelowo and Rosamund Pike.

Oyelowo is in talks to play Seretse Khama, who in 1965 became independent Botswana’s first president. He was also kgosi (king) of the Bamangwato people, having been crowned at the age of four in 1925. Pike is in line to star as Ruth Williams, who would go on to be the first lady of Botswana between 1966 and 1980.

The marriage was vehemently opposed by the racist South African government, which bullied Britain’s ruling Labour party into exiling the royal couple from Bechuanaland in 1951. The king’s uncle and sometime regent, Tshekedi Khama, also tried and failed to have his nephew deposed. Williams, meanwhile, proved suprisingly popular in Africa.

Titled A United Kingdom, the film has secured up-and-coming British film-maker Amma Asante to direct. The London-born director and screenwriter is known for the much-praied 2013 drama Belle, starring Gugu Mbatha-Raw, Tom Wilkinson and Matthew Goode, which details the life of a mixed-race daughter of a British Royal Navy officer living in 18th-century England. She will work from a screenplay by Five Minutes of Heaven’s Guy Hibbert.

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“Amma and Rosamund are two of the most exciting talents working in film today,” said Oyelowo, also a producer on the drama. “I’ve worked with both of them before and so my excitement about them joining A United Kingdom stems from a knowledge of just how inspiring they are to work with and how much daring and beauty they will bring to this epic love story.”

Both Oyelowo and Pike are coming off awards season buzz for their films Selma and Gone Girl, respectively. Pike was nominated in the best supporting actress category for her turn as a missing woman in David Fincher’s adaptation of the bestselling Gillian Flynn novel, while Oyelowo was considered unfortunate to miss out on an acting nod for his turn as Martin Luther King Jr in Ava DuVernay’s historical drama.

• This article was amended on 29 May 2015. An earlier version said Seretse Khama was “independent Botswana’s first black president” and “the country’s kgosi (king)”.